Horton

Re: Estimating HugePages Requirements?

Michael Paquier <michael@paquier.xyz>

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From: Michael Paquier <michael@paquier.xyz>
To: "Bossart, Nathan" <bossartn@amazon.com>
Cc: Fujii Masao <masao.fujii@oss.nttdata.com>, Justin Pryzby <pryzby@telsasoft.com>, Andres Freund <andres@anarazel.de>, Magnus Hagander <magnus@hagander.net>, Mark Dilger <mark.dilger@enterprisedb.com>, Don Seiler <don@seiler.us>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2021-09-10T02:03:05Z
Lists: pgsql-hackers 
On Thu, Sep 09, 2021 at 09:53:22PM +0000, Bossart, Nathan wrote:
> For 0002, I have two small concerns.  My first concern is that it
> might be confusing to customers when the runtime GUCs cannot be
> returned for a running server.  We have the note in the docs, but if
> you're encountering it on the command line, it's not totally clear
> what the problem is.

Yeah, that's true.  There are more unlikely-to-happen errors that
could be triggered and prevent the command to work.  I have never
tried using error_context_stack in a code path as early as that, to be
honest.

> Running these commands with log_min_messages=debug5 emits way more
> information for the runtime-computed GUCs than for others, but IMO
> that is alright.  However, perhaps we should adjust the logging in
> 0002 to improve the default user experience.  I attached an attempt at
> that.

Registered bgworkers would generate a DEBUG entry, for one.

> I'm not tremendously happy with the patch, but I hope that it at least
> helps with the discussion.

As far as the behavior is documented, I'd be fine with the approach to
keep the code in its simplest shape.  I agree that the message is
confusing, still it is not wrong either as we try to query a run-time
parameter, but we need the lock.
--
Michael

Commits

  1. Silence extra logging when using "postgres -C" on runtime-computed GUCs

  2. doc: Improve postgres command for shared_memory_size_in_huge_pages

  3. Introduce GUC shared_memory_size_in_huge_pages

  4. Support "postgres -C" with runtime-computed GUCs

  5. Make shared_memory_size a preset option

  6. Introduce GUC shared_memory_size

  7. Move the shared memory size calculation to its own function

  8. Add new GUC, max_worker_processes, limiting number of bgworkers.